translated from Spanish: Neanderthals’ thumbs were adapted to hold tools with handle

World.- A team led by the University of Kent in the UK, which has analyzed Neanderthal remains guarded by several museums, claims that they were able to use power grips. This implies that they adapted their thumbs to hold tools in the same way that we take a hammer, between the fingers and palm of the hand, with the force of direction of the thumb.
An international team of scientists has studied the differences between Neanderthals and modern humans when it comes to using hand joints to grab objects. Through 3D analysis, they mapped the joints between the bones responsible for the movement of the thumb – trapezometacarpian joint – of five Neanderthal individuals and compared them to measurements taken from the remains of five early modern humans and 50 recent modern adults.
«These grips would be advantageous for the use of some tools, such as musteriense spears or scrapers,» says Ameline Bardo
«The thumb base joint of Neanderthal fossils is flatter, with a smaller contact surface between the bones, which best fits an extended thumb placed along the side of the hand. This thumb posture suggests the regular use of power grips, which is what we use when holding tools with handles, such as a hammer. These grips would be advantageous for the use of some tools, such as Musteriense spears or scrapers,» Ameline Bardo, a postdoctoral Associate researcher at the University of Kent School of Anthropology and Conservation, says. The study is published in Scientific Reports.
The authors found covariance in the shape and orientation of the joints of the trapeziometacarpian joint. This suggests different repetitive thumb movements in Neanderthals, compared to modern humans.
«Human thumbs have joint surfaces that are generally larger and more curved, which is an advantage when gripping objects between the finger and thumb pads, known as precision grip,» Bardo adds.
Study the morphology of the hand as a whole
Previous research had quantified how the shapes of thumb bones vary in Neanderthals and modern humans, as well as in many other fossil human relatives (hominids). However, these works typically analyzed the bones in isolation.
This variation between modern humans and Neanderthals may reflect different activities that each species routinely performed with the hands
«Our study is novel by observing how the variation in the shapes and orientations of the different bones and joints are related together. The movement and burden of the thumb is only possible because these bones, as well as ligaments and muscles, work together, so they must be studied together,» he continues.
Scientists used a three-dimensional analysis of the shape of bones called geometric morphology that allowed them to quantify how joint shapes and orientations vary across different bones. «Specifically we observe shape covariance between the trapezium (a wrist bone at the base of the thumb) and the proximal end of the first metacarpal (the first thumb bone that joins the wrist) in Neanderthals (Homo neanderthalensis), compared to early and recent humans (Homo sapiens),» the researcher says.
To reach this conclusion, scientists placed landmarks on all bone surfaces and used them to measure the extent to which the shape change on one side of the joint, at the base of the thumb, corresponded to the other side. «In this way we can understand which positions of the thumb would be favored by the different shapes of the joints. Our results suggest that this favored thumb position was different in humans and Neanderthals,» Bardo stresses.
This variation between modern humans and Neanderthals may reflect, according to experts, different activities that each species routinely carried out with its hands. For the study they included all available Neanderthal hand fossils, which retain both a trapeze and a first metacarpal, but fossils are scarce and difficult to find.
«Without a time machine, we will always struggle to know for sure how our fossil relatives used their hands, tools, and how they behaved. We often have to make assumptions about behavior in the past using living people, which comes with its own prejudices. There are many ‘unknowns’ in paleoanthropology. However, by using more sophisticated methods (such as analyzing 3D shapes we use in this work), we hope to get as much information as possible from the fossils we have,» concludes the scientist.
Comparing fossil morphology between neanderthals and modern humans can provide a greater understanding of the behaviors of our former relatives and the use of early tools.

Original source in Spanish

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